1. Field of the Invention
The present invention relates to a disposable card used for prepaid cards, admission tickets, or a disposable card-type material used for letters of guarantee, securities and the like, and more particularly to a card whose entire composition has decomposition properties.
2. Background Art
Currently, cards are utilized in wide fields such as ID cards or membership cards identifying social standing, cash cards, credit cards, prepaid cards, passes or traffic tickets having monetary values, or letters of guarantee, securities and the like.
Cards which have increased most in the number of cards utilized among those as mentioned above are the so-called prepaid cards in which monetary value information has been recorded equivalent to a certain amount of money previously paid.
Usually, such cards after being sold to users are discarded when users use up the full amount of money recorded. Generally such prepaid cards comprise plastics such as polyethylene terephthalate (PET) resin as a card base material, in which pattern and character information are printed on the card base material, while digital information is recorded on a magnetic recording portion or an optical recording portion provided on the card base material. Although such plastic cards after being fully used are currently disposed of by incineration or by landfill as a waste, plastic waste, when being incinerated, causes burning temperature to become higher, leading to problems with the durability of incinerators and with the environmental pollution due to combustion gas, while plastic waste, when being used for landfill, does not decompose, remaining as it is, so that it remains permanently as refuse, leading to problems with the effect on natural environment.
Heretofore, there have been produced and utilized cards employing paper as their base material, which paper is easy to be discarded for incineration or landfill and less expensive in manufacturing cost, so that paper has been considered to be an optimum card material with respect to the above-mentioned, currently-discussed environmental problems.
Also recently, as disclosed in Japanese Laid-Open Patent Application No. 57-150393, Japanese Laid-Open Patent Application No.59-220192, Japanese Laid-Open Patent Application No.51-93991, Japanese Laid-Open Patent Application No.63-260912 and Japanese Laid-Open Patent Application No.57-150393, plastics, which are decomposable under natural environment such as light or underground condition, have been developed, have been particularly for throwaway products, and have now commercially been available partly. With respect to the cards field, Japanese Laid-Open Patent Application No.5-42786 and Japanese Laid-Open Patent Application No.5-85088 by the present applicant disclose that decomposable plastics are used for card base material. Problems that the Invention is to solve
However, where paper is used for card base material as shown in FIG. 3, considering the suitability for cards, such as durability, bending resistance, water resistance, chemical resistance, waterproofness, surface smoothness, glossiness and workability, paper is inferior in function in all respects. Thus sole paper application is limited to a temporary one such as traffic tickets, admission tickets and railway tickets, and not suitable for the above-mentioned prepaid cards used for a certain period. For such a purpose, although it is considered that an outer layer of plastics such as polyethylene, polypropylene, polyvinyl chloride and polyethylene terephthalate, or those other than plastics such as aluminum foil are laminated as a protective layer on a paper bass material as shown in FIG. 4, these cards are inferior in discardability and have a disadvantage not significantly different from plastic cards.
A card in which the base material itself is composed of a decomposable plastic gradually decomposes due to its plastic function after being discarded. However, cards are to be produced with consideration to convenience in themselves and to a problem with card manufacture, so that where a decomposable plastic is used only for a card base material, problems as shown below exist.
The problems exist in that first a card is required to have a certain thickness from the strength and user-friendliness points of view, so that when the card is molded, a warpage develops on the card surface; that the decomposition of a decomposable plastic requires a longer time corresponding to such thickness; and that since a decomposable plastic is expensive, the card itself becomes expensive.